Method for fabricating a dimpled concave dispenser cathode incorporating a grid

ABSTRACT

Methods for fabricating concave dimpled dispenser cathodes are disclosed. A multicell groove pattern is formed in the concave face of the cathode blank. An array of concave dimples are formed in the cellular regions of the concave emitter face bounded by the cells of the groove pattern. A multicell grid structure is incorporated into the groove pattern. The groove pattern is formable by photoetching, electrical discharge machining or by milling. The grid structure may be brazed into the grooves or merely supported therein in noncontacting relation therewith.

United States Patent Inventors George V. Mirarn Daly City; Gerhard B.Kuelrne, Santa Clara, both of, Calif. Appl. No. 833,458 Filed June 16,1969 Patented July 27, 1971 Assignee Varian A sociates Palo Alto, Calif.

METHOD FOR FABRICATING A DIMPLED CONCAVE DISPENSER CATHODE INCORPORATINGA GRID 9 Claims, 9 Drawing Figs.

US. Cl 29/25.l8, v 29/2S.l4,313/337 Int. Cl H0lj 9/ 16, v H0 1 j 9/44Field ofSearch 29/25.l8,

References Cited UNITED STATES PATENTS 2,864,028 12/1958 Coppola 313/337X 2,977,496 3/1961 313/69 3,067,486 12/1962 29/25. 1 8 3,139,552 6/1964313/339 3,293,487 12/1966 29/25. 14 X Primary Examiner.lohn F CampbellAssistant ExaminerRona1d J. Shore Attorneys-Stanley Z. Cole and GeraldL. Moore ABSTRACT: Methods for fabricating concave dimpled dispensercathodes are disclosed. A multicell groove pattern is formed in theconcave face of the cathode blank. An array of concave dimples areformed in the cellular regions of the concave emitter face bounded bythe cells of the groove pattern. A multicell grid structure isincorporated into the groove pattern. The groove pattern is formable byphotoetching, electrical discharge machining or by milling. The gridstructure may be brazed into the grooves or merely supported therein innoncontacting relation therewith.

PATENTEU JUL27T971 V sum 2 0F 2 FORMATION coNcAvE CATHODE DISPENSERBLANK INCORPORATION-OF 5 GRID INTO GRID SHAPED GROOVE PATTERN (a) (b)(0) FIG-7 (a) AFFIX APPLY CHEMICALLY MASKING PHoTo-ENuLsLoN mffi EToH DT0 T0 BLANK GROOVE BL THROUGH MASK PATTERN Y I L REMOVE LHPREPNATELNcoRPoRATE DIMPLE MALLEABLE 'L gg 'y 'MPREGNANT NATERLAL PATTERN (e)(f) (g) (h) (a) (b) (0) FIG. 8 (a) AFFIX APPLY REMOVE MACHINE A fi wgMASKING MASKING Q QYE YQ A.

BLANK PA'NT NAcHLNE ELECTRICAL DISCHARGE LNvENToRs' FIG 9 MACHINE TooLGEORGE v. NLRAN GERHARD-BKUEHNE Qeu BY cATHooE BLANK ATToR EY I METHODFOR FABRICATING A DIMPLED CONCAVE DISPENSER CATI IODE INCORPORATING AGRID DESCRIPTION OF THE PRIOR ART Heretofore, ithas been proposed toprovide a multicell grid structure on or in the surface of a concave anddimpled cathode emitter with the cells of the grid structure being inalignment with apertures in a control grid. Such a cathode is disclosedand claimed in copending U.S. Pat. application Ser. No. 650,893 filedJuly 3, 1967 and assigned to the same assignee as the present invention.Such cathodes are especially useful in electron guns of high-convergencehigh-power linear beam tubes since control grid current interception isgreatly reduced. This follows since the grid structure in or on thecathode helps to focus the electron beamlets through the alignedapertures of the control grid. Moreover, the focusing grid structurehelps to inhibit electron emission from the regions of the cathode inregistration with the webs of the control grid. However, heretoforepractical production methods for fabricating dispenser cathodesincorporating such focusing grid structures have not been known.

SUMMARY OF THE PRESENT INVENTION The principal object of the presentinvention is the provision of an improved method for fabricating aconcave dimpled dispenser cathode having a grid structure incorporatedtherein.

One feature of the present invention are the steps of forming amulticell groove pattern in the concave face of a dispenser cathodeblank to accommodate a multiapertured grid structure and forming anarray of dimpled facets in the concave face of the cathode blank, suchfacets each being bounded by individual cells of the multicell groovepattern.

Another feature of the present invention is the same as the precedingfeature wherein the step of forming the groove pattern comprises thestep of milling the grooves in the concave face of the cathode blank.

Another feature of the present invention is the same as the firstfeature wherein the step of forming the groove pattern compriseschemically etching the groove pattern in the concave face of the cathodeblank.

Another feature of the present invention is the same as the firstfeature wherein the step of electrically discharge machining the groovepattern with a discharge defining electrode having a pattern conformingto at least a portion of the groove pattern to be formed.

Other features and advantages of the present invention will becomeapparent upon a perusal of the following specification taken inconnection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is fragmentary longitudinalsectional view of an electron gun fabricated by methods incorporatingfeatures of the present invention;

FIGS. 2 and 4 are enlarged detail views of alternative embodiments tothat portion of the structure of FIG. 1 delineated by lines 22 and 4-4,

FIGS. 3 and are enlarged detail views of portions of FIGS. 2 and 4delineated by lines 3-3 and 5-5, respectively,

FIG. 6 is a perspective flow diagram depicting a method of the presentinvention for fabricating dispenser cathodes.

FIG. 7 is a flow diagram in block diagram form depicting acathode-fabricating method of the present invention;

FIG. 8 is flow diagram in block diagram form depicting certain steps ina method of the present invention; and

FIG. 9 is a sectional view of a tool of an electrical discharge machinedepicting how it is employed in a method of the 3 present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, thereis shown an electron gun I employing a concave dispenser cathode emitter2. The emitter is of the type disclosed in the aforecited U.S. Pat.application Ser. No. 650,893 and briefly is a spherical section ofbariumimpregnated porous tungsten having a multitude of closely packeddimpled facets 3 in the concave face 4 of the emitter 2. A centrallyapertured anode electrode 5 faces the concave face 4 of the emitter 2. Amultiaperturcd control grid 6 is disposed closely overlying andconforming to the shape of the concave surface 4. The apertures 7 of thecontrol grid 6 are preferably hexagonal and disposed in registrationwith the dimpled facets 3, Le, center of grid openings 7 falls on anelectron trajectory leaving the center of facet 3.The facets 3 may be ofcircular or hexagonal boundary configuration with spherically concavesurfaces of substantially lesser radius of curvature than the radius ofcurvature for the composite concave face 4.

A focus grid structure 8, having a configuration substantially identicalto that of control grid 6, is incorporated into the concave surface 4 ofthe emitter 2 such that the web portions of focus grid 8 are inalignment with the similar web portions of the control grid 6. The focusgrid 8 is positioned within a grid shaped groove pattern 9 in theconcave surface 4 of the emitter. The grid 8 may be supported innoncontacting relation with respect to the grooves or it may be affixed,as by brazing, to the grooves. These two alternatives are depicted ingreater detail in FIGS. 2-5 below. The focus grid serves to focus theindividual electron beamlets through the corresponding aperture 7 incontrol grid 6 in a substantially nonintercepting manner. The focus grid8, as of molybdenum, is coated with an electron-emission-inhibitingmaterial, such as, carbon, titanium, zirconium, iridium, etc., toprevent current interception on the control grid 6 because the coatinginhibits emission from those portions of the cathode surface 4 whichwould have electron trajectories to intercept the web members of grid'6.

After the beamlets pass through apertures 7 they converge into a unitarybeam which passes through the central opening in anode 5. In a typicalexample, the gun 1 produces a beam of 1 amp at 10 kv. with amicroperveance of 1.0 and cathode loading current density of L2 amps/cm.2. Grid interception was 0.8 percent of the beam current.

Referring now to FIGS. 2 and 3, there is shown one embodiment of thedispenser cathode 2. In this embodiment, focus grid structure 8 issupported at its periphery from a relatively heavy tubular thermallyconductive support 11 for heat sinking and cooling the grid 8. The grid8 is supported in noncontacting relation within the groove pattern 9 toinhibit thermal conduction from the cathode 2, which normally operateswithin the range of 900 to l,l00 C, to the grid 8. The noncontactingrelation also serves to inhibit migration of barium impregnant from thecathode 2 to the grid 8. In a typical example, the grooves 9 have awidth of 0.01 6 inch and a depth of 0.005 inch and the grid 8 has a webwidth of 0.010 inch and a depth in the direction of the beam of 0.009inch and is separated from the bottom of the groove 9 by 0.001 inch.

Referring now to FIGS. 4 and 5, there is shown a second embodiment ofthe dispenser cathode 2 wherein the grid 8 is supported from the cathodebody via brazed joints 12 between the bottom of the grooves 9 and theabutting surface of the grid 8. Suitable braze materials includemolybdenum-nickel or molybdenum-ruthenium mixes.

Referring now to FIG. 6, there is shown a flow diagram depicting thesteps of the present invention for fabricating dispenser cathodes havinggrid structures incorporated therein. In the method, a sphericallyconcave dispenser cathode blank 2, such as porous tungsten impregnatedwith a malleable material such as copper or plastic has its concavesurface 4 grooved, in step (a), with a multicell hexagonal pattern ofgrooves 9 such groove pattern conforming to the grid pattern of thecontrol grid 6 and to the pattern of the focus grid 8 to be located inthe grooves 9. The grooves 9 may be formed as by chemical etching,milling, or by electrical discharge machining in the manner more fullydescribed below with regard to FIGS. 79.

After the grid pattern of grooves 9 is formed, the dimpled facets 3 areformed, in step (b), in each of the cells of the groove pattern 9. Thedimples 3 are formed either by machining or by electrical dischargemachining.

In step (c), the focus grid structure 8 is incorporated into the groovepattern 9 either in noncontacting relation, as described above withregard to FIGS. 2 and 3, or in contacting relation as described withregard to FIGS. 4 and 5.

Referring now to FIG. 7, the general method of FIG. 6 is described ingreater detail as employing chemical etching to form the grid-shapedpattern of grooves 9 in the cathode blank 2.

More specifically, in step (a), a masking grid structure substantiallyidentical to grid 8, in fact it can be grid 8, is affixed to the concavesurface 4 of the cathode blank 2, as by an adhesive or by clamping. Instep (b), an acid resistant emulsive coating, such as A-Z l l 1 photoresist coating manufactured by Shipley Company, is applied to theconcave surface 4 of the cathode blank 2 through the openings in themasking grid. In step (c), the masking grid is removed leaving theexposed grid pattern in the cathode blank surface 4.

In step (d), the surface 4 is treated with a chemical acid etch such aspotassium ferrocyanide and caustic for etching the groove pattern 9 intothe concave surface 4. In step (c) the surface 4 is dimpled as abovedescribed. In step (b), the malleable impregnant of the porous tungstenbody is removed, as by chemical etching or heating to boil out theimpregnant.

In step (g), the porous tungsten body is impregnated with electronemissive material, such as barium, ferrocyanidc conventional manner. Instep (h), the grid structure 8 with its electron-emissioninhibitingcoating is incorporated in the grid pattern of grooves 9 either in thenoncontacting manner, as described above with regard to FIGS. 2 and 3,or in contacting relation, as described above with regard to FIGS. 4 and5. The dimpling step (e) can be performed either before or afterincorporation of the grid 8. If it is performed after incorporation ofthe grid 8, the dimpling tool is merely inserted through the respectiveaperture in grid 8.

Referring now to FIG. 8, there is shown the steps in an alternativemethod for forming the pattern of grooves 9 in the cathode blank 2. Morespecifically, steps (ad) replace steps (a-d) in the process of FIG. 7.In step (a), a masking grid is affixed to the cathode blank 2, as instep (a) of the method of FIG. 7. In step (b), a marking dye or paint isapplied through the holes in the masking grid to indicate the desiredgrid pattern for the grooves 9 by the unpainted web pattern in thepainted surface. In step (c), the masking grid is removed to expose thedesired grid pattern markings. In step (d), the concave surface 4 ismilled by a milling machine along the unpainted lines of the desiredgrid pattern. The remainder of the process of manufacture remains thesame as described with regard to FIG. 7.

Referring now to FIG. 9, there is shown an alternative method forforming the grid pattern of grooves 9 in the cathode surface 4. In thismethod, steps (a--d) of the method of FIG. 7 are replaced by the step ofelectrically discharge machining the pattern of grooves 9 in the concavesurface 4 of the cathode blank 2. The electrical discharge defining electrode tool 15 has a spherically curved surface I6 conforming to thesurface 4 of the cathode blank 2. Formed on the surface 16 of the tool15 is a raised grid pattern 17 conforming to the grid pattern of thegrooves 9 to be formed in the cathode blank 2. The electrical dischargemachining tool I is then moved into the surface 4 of the cathode blank 2to machine the grid pattern of grooves 9 therein. The remainder of thismethod is the same as that previously described above with retion andmany ap arently widely different embodiments of this lnvention coud bemade without departing from the scope thereof, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What we claim is:

1. In a method for fabricating a dimpled dispenser cathode for aconvergent stream electron gun the steps of, forming a multicell groovepattern in the concave face of a dispenser cathode blank, such multicellgroove pattern conforming generally to the web pattern of amultiapertured control grid to be employed over the concave emissivesurface of the dispenser cathode, forming an array of concave dimpledemissive facets in the concave face of the cathode blank, each of theindividual facets being located such as to be bounded by an individualcell of the multicell groove pattern, and incorporating a multiaperturedgrid structure in the groove pattern, such grid structure having a webpattern conforming generally to the groove pattern and to the webpattern of the control grid.

2. The method of claim I wherein the step of forming the multicelledgroove pattern in the concave face of the dispenser cathode blankcomprises the step of marking the concave face to be grooved to indicatethe'pattern of the desired grooves, and milling the grooves in theconcave face according to the marked pattern. I

3. The method of claim 1 wherein the step of forming the multicelledgroove pattern in the concave face of the dispenser cathode blankcomprises the step of electrically discharge machining the concave facewith a tool having a discharge defining electrode pattern conforming toat least a portion of the desired groove pattern to be formed in theconcave face of the dispenser cathode blank.

4. The method of claim 1 wherein the step of forming the, multicelledgroove pattern in the concave face of the dispenser cathode blankcomprises the step of, chemically etching the groove pattern in theconcave face of the dispenser cathode blank.

5. The method of claim 1 wherein the cathode blank into which the groovepattern is to be formed comprises a porous tungsten body with the poresinfiltrated with a malleable material, and including the steps ofremoving the malleable material from the grooved cathode blank to leavea porous metal blank, and infiltrating the pores of the metal blank withelectron emissive material to form a dispenser cathode body.

6. The method of claim 5 wherein the step of incorporating the gridstructure into the groove pattern includes the steps of, locating theweb of the grid structure in the groove pattern, and brazing the gridstructure to the grooved cathode body.

7. The method of claim 5 including the step of, coating the gridstructure to be incorporated in the groove pattern of the dispensercathode blank with an electron-emission-inhibiting coating.

8. The method of claim 4 wherein the step of chemically etching thegroove pattern includes the steps of, positioning a masking gridstructure, having the desired grid pattern to be formed in the cathode,adjacent the concave face of the cathode blank, coating the gridstructure and exposed positions of the masked concave face of thecathode blank with an acid-resistant emulsion, removing the masking gridstructure to expose the surface of the cathode blank masked by themasking grid structure, and chemically etching the exposed surfaces inthe concave face of the cathode blank to form the desired groovepattern.

9. The method of claim 1 wherein the individual cell pattern of thegrooves fonned in the concave face of the cathode blank is hexagonal.

1. In a method for fabricating a dimpled dispenser cathode for aconvergent stream electron gun the steps of, forming a multicell groovepattern in the concave face of a dispenser cathode blank, such multicellgroove pattern conforming generally to the web pattern of amultiapertured control grid to be employed over the concave emissivesurface of the dispenser cathode, forming an array of concave dimpledemissive facets in the concave face of the cathode blank, each of theindividual facets being located such as to be bounded by an individualcell of the multicell groove pattern, and incorporating a multiaperturedgrid structure in the groove pattern, such grid structure having a webpattern conforming generally to the groove pattern and to the webpattern of the control grid.
 2. The method of claim 1 wherein the stepof forming the multicelled groove pattern in the concave face of thedispenser cathode blank comprises the step of marking the concave faceto be grooved to indicate the pattern of the desired grooves, andmilling the grooves in the concave face according to the marked pattern.3. The method of claim 1 wherein the step of forming the multicelledgroove pattern in the concave face of the dispenser cathode blankcomprises the step of electrically discharge machining the concave facewith a tool having a discharge defining electrode pattern conforming toat least a portion of the desired groove pattern to be formed in theconcave face of the dispenser cathode blank.
 4. The method of claim 1wherein the step of forming the multicelled groove pattern in theconcave face of the dispenser cathode blank comprises the step of,chemically etching the groove pattern in the concave face of thedispenser cathode blank.
 5. The method of claim 1 wherein the cathodeblank into which the groove pattern is to be formed comprises a poroustungsten body with the pores infiltrated with a malleable material, andincluding the steps of removing the malleable material from the groovedcathode blank to leave a porous metal blank, and infiltrating the poresof the metal blank with electron emissive material to form a dispensercathode body.
 6. The method of claim 5 wherein the step of incorporatingthe grid structure into the groove pattern includes the steps of,locating the web of the grid structure in the groove pattern, andbrazinG the grid structure to the grooved cathode body.
 7. The method ofclaim 5 including the step of, coating the grid structure to beincorporated in the groove pattern of the dispenser cathode blank withan electron-emission-inhibiting coating.
 8. The method of claim 4wherein the step of chemically etching the groove pattern includes thesteps of, positioning a masking grid structure, having the desired gridpattern to be formed in the cathode, adjacent the concave face of thecathode blank, coating the grid structure and exposed positions of themasked concave face of the cathode blank with an acid-resistantemulsion, removing the masking grid structure to expose the surface ofthe cathode blank masked by the masking grid structure, and chemicallyetching the exposed surfaces in the concave face of the cathode blank toform the desired groove pattern.
 9. The method of claIm 1 wherein theindividual cell pattern of the grooves formed in the concave face of thecathode blank is hexagonal.